PT sups aren't suppose to return to hourly status. A few years ago we had somebody get hired, work a few weeks, then get poop canned after UPS realized they had been a PT sup in the 1990s. BUT... that was during the height of the recession when landing a job at McDonald's was a big deal around here. UPS is so desperate for bodies here today that it plans to charter a bus into the Projects to get additional lift for peak season (boy, that sounds like a good idea). Thus, I suspect they'd look the other way if that situation arose today.
In your situation, they WILL find out; you will give them your SSN eventually after all (which will link you to the PT/management pension, and you'll maintain previous credit, so it may be a good thing). But as long as you're honest throughout the process... I wouldn't let it bother me.